The present invention relates to the field of electronic position sensor assemblies and the use of position sensor signals in a control system. The present invention has particular application to an electronic engine-control system, especially such a system which utilizes electronic spark distribution and/or electronic fuel control signal distribution so as to sequentially provide control signals for the spark occurrence/fuel injection for each cylinder of a multi-cylinder engine.
Prior engine control systems are known in which spark timing occurrence control signals and fuel injection control signals are produced in accordance with engine speed. Typically these control signals are produced in accordance with engine cycle position signals derived by sensing the angular position of projections/slots on a wheel synchronously rotated by the engine crankshaft. Such wheels are typically referred to as toothed wheels, and reluctance, Hall effect or optical sensors are utilized to sense the angular position of such wheels and thereby provide position signals corresponding to various engine cycle positions.
Typically, three pieces of information are required for engine control systems such as those noted above. First, an accurate high resolution engine speed and position signal is desired This is typically achieved by providing a large number of individual teeth on the periphery of a wheel to be rotated synchronously by the engine crankshaft such that a large number of individual pulses are produced. The repetition rate of these pulses is directly related to engine speed, and pulse time occurrence is indicative of engine cycle position. In addition, in some systems it is necessary to determine the top-dead center (TDC), or other reference, position of the piston in each one of the cylinders of a multiple cylinder engine which is to be controlled by the engine control system. Some prior systems utilize a separate sensing element to provide this top-dead center reference position information by sensing a projection/slot on the rotating wheel (or on a different wheel) which is separate from the large number of individual teeth already being sensed to produce the high resolution engine speed/position signal. In addition, for implementing electronic spark control signal distribution or fuel injection control signal distribution, it is also necessary to provide a reference cylinder identification signal (CID) which identifies one of the multiple cylinders to be controlled as a reference cylinder as opposed to any other of the cylinders. This signal is then used to insure proper initial routing (distribution) of control signals to the various cylinders while the TDC signal may control the timing of the subsequent sequential routing of control signals
Some prior systems have utilized three separate sensors to provide the three types of information required for systems such as those described above. Obviously providing three different sensors and three different sets of projections/slots to be sensed is not desirable from either a cost or system complexity point of view. Some prior systems have used missing tooth or special tooth detection systems to provide two of the three pieces of information. U.S. Pat. No. 4,628,269 to Hunninghaus et al. shows a prior system to provide both the high resolution signal and the CID signal. Other systems, such as U.S. Pat. No. 4,338,813 to Hunninghaus et al. and U.S. Pat. No. 4,338,906 to Bolinger, have used two or more sensors to provide TDC and CID signals, but then no high resolution position signals are produced.
What is needed is a sensor system to reliably produce all three types of required signals without using an excessive number of sensors and without using an extensive amount of circuitry or requiring extensive microprocessor calculation time. Preferably such a system should also be able to produce the required high resolution signal and reference signals even if a sensor element fails. Some prior systems, such as U.S. Pat. No. 4,658,786 to Foss et al., take some corrective action in case of a detected fault, but typically the high resolution signal is lost if any sensing element producing that signal fails and/or such systems provide extra circuitry for normally using a different signal as a reference signal and guard against loss of this different reference signal by using, if a fault, the original reference signal. Some systems use simplified coincidence detection circuitry, such as U.S. Pat. No. 4,385,605 to Petrie et al., to provide a reference signal, but in the event of a sensing element failure, no reference signal is provided.